Re: [PATCH] pnfsblock: init pg_bsize properly

[Peng Tao <bergwolf@gmail.com>]

Hi, Benny and Boaz,

On Wed, Aug 17, 2011 at 3:15 PM, Benny Halevy <bhalevy@tonian.com> wrote:
>
> On 2011-08-17 00:05, Boaz Harrosh wrote:
>> On 08/12/2011 06:04 PM, Peng Tao wrote:
>>> pg_bsize is server->wsize/rsize by default. We would want to use the lseg length.
>>>
>>
>> Hi
>>
>> What is the problem you are trying to solve with this patch?
>>
>> From what I understand the only place that actually cares about
>> pg_bsize is nfs_generic_pg_test() which is only used in MDS
>> read/write. In the pNFS RW, the LD and pnfs has it's own .pg_test()
>> check that should not concern with pg_bsize (Unless for pnfs-files
>> which does). So the idea is that pg_bsize is the maximum set by
>> MDS server in regard to IO through MDS. And it should not be changed
>> by client.
>>
>> If it is not what you see then we should fix it. But should never
>> override MDS wsize/rsize.
In pnfs_do_multiple_reads/pnfs_do_multiple_writes, data->mds_ops will
be set as desc->pg_rpc_callops, which is determined in
nfs_generic_flush/nfs_generic_pagein according to desc->pg_bsize. For
blocklayout, we wouldn't want to set data->mds_ops to
partial_read/write ops, so I write the patch to use lseg length as
pg_bsize.

LD can override pg_bsize in pg_init because
nfs_pageio_reset_read_mds/nfs_pageio_reset_write_mds will reset it to
server rsize/wsize if pnfs is not tried.

Sorry that I didn't explain it clearly in the commit log...


>
> I second that.
>
> Benny
>
>>
>>> Signed-off-by: Peng Tao <peng_tao@emc.com>
>>> ---
>>>  fs/nfs/blocklayout/blocklayout.c |   20 ++++++++++++++++++--
>>>  1 files changed, 18 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
>>> index 36648e1..9143e61 100644
>>> --- a/fs/nfs/blocklayout/blocklayout.c
>>> +++ b/fs/nfs/blocklayout/blocklayout.c
>>> @@ -919,14 +919,30 @@ bl_clear_layoutdriver(struct nfs_server *server)
>>>      return 0;
>>>  }
>>>
>>> +static void bl_pg_init_read(struct nfs_pageio_descriptor *pgio,
>>> +                        struct nfs_page *req)
>>> +{
>>> +    pnfs_generic_pg_init_read(pgio, req);
>>> +    if (pgio->pg_lseg)
>>> +            pgio->pg_bsize = pgio->pg_lseg->pls_range.length;
>>> +}
>>> +
>>> +static void bl_pg_init_write(struct nfs_pageio_descriptor *pgio,
>>> +                         struct nfs_page *req)
>>> +{
>>> +    pnfs_generic_pg_init_write(pgio, req);
>>> +    if (pgio->pg_lseg)
>>> +            pgio->pg_bsize = pgio->pg_lseg->pls_range.length;
>>> +}
>>> +
>>>  static const struct nfs_pageio_ops bl_pg_read_ops = {
>>> -    .pg_init = pnfs_generic_pg_init_read,
>>> +    .pg_init = bl_pg_init_read,
>>>      .pg_test = pnfs_generic_pg_test,
>>
>> I see here that you do not override .pg_test. This is your problem
>> look at objio_osd::objio_pg_test() it checks for similar boundaries
>> at the objects side. This is where you need to do these checks
>> for blocks as well.
For blocklayout, we don't need to force each IO under a certain size.
Currently (w/ and w/o this patch) the lseg coverage is the only
constraint for pagelist length. So pnfs_generic_pg_test is enough for
blocklayout.

Thanks,
Tao

>>
>>>      .pg_doio = pnfs_generic_pg_readpages,
>>>  };
>>>
>>>  static const struct nfs_pageio_ops bl_pg_write_ops = {
>>> -    .pg_init = pnfs_generic_pg_init_write,
>>> +    .pg_init = bl_pg_init_write,
>>>      .pg_test = pnfs_generic_pg_test,
>>
>> Same here
>>
>>>      .pg_doio = pnfs_generic_pg_writepages,
>>>  };
>>
>> Thanks
>> Boaz
>> --
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>